The present invention relates to photosensitive media for electrophotography, and more particularly to an electrophotographic photosensitive medium having a photosensitive layer which comprises a styryl compound as a main component.
Widely known as photosensitive media for electrophotography are those of function-divided types comprising a charge generating layer and a charge transporting layer which are formed on an electrically conductive substrate, and those of dispersion types comprising a photoconductive layer formed on a substrate and prepared by dispersing photoconductive particles in resin.
With the function-divided type, separated layers work dividedly to serve the basic functions of the photosensitive medium, i.e. generation of charge carriers and transport of the charges, to provide a photosensitive layer chargeable to a high surface potential and exhibiting great charge retentivity, high photosensitivity and stabilized repetition characteristics. Many compounds are known as charge generating materials and as charge transporting materials for use in the photosensitive media of the function-divided type. For example, various organic photoconductors of low molecular weight have been proposed for use in charge transporting layers. More specifically, U.S. Pat. No. 3,189,447 proposes use of 2,5-bis (p-diethylaminophenyl)-1,3,4-oxadiazole, but this compound has only a poor compatibility with binders and is liable to separate out as crystals. Further U.S. Pat. No. 3,820,989 discloses use of diarylalkane derivatives having a high compatibility with binders. However, the photosensitive medium containing the derivatives undergoes variations in sensitivity when repeatedly used, and is still required to be improved in initial sensitivity and residual potential characteristics, as well as in sensitivity variations and durability for repeated use.